[TurboSnap] Add a flag to skip builds with the same commit, rather than rebuild entirely.

[tmeasday]

Some use cases lead to repeated builds on the same commit for CI-related reasons, rather than user-initiated rebuilds.

It is useful in such cases to treat the build as a skipped build rather than do a full rebuild.

[tmeasday]

@ghengeveld have we already sorted this out?

[ghengeveld]

I don't think so

[thafryer]

@tmeasday Closing this! I think we already have this behavior without needing to add a flag. Feel free to re-open if not!